That is slick and creepy
Re Rose petals, I've never seen them in a regular supermarket or even Holland and Barret. Just Waitrose. Otherwise you need to buy them online among with any other edible flowers. I follow a few vegan foodies who use a lot of edible flowers in their baking and cooking but they grow it themselves. Also as a warning, something I learned from a vegan baker and cook is that a lot of bakers use any old plants to decorate cakes (especially wedding cakes) without wrapping the stem or worse, checking it's an edible plant. In some cases that is quite dangerous as some edible plants are actually quite toxic. If you are buying a cake with flowers always check first with the baker and then Google.
Until she catches up on Tattle, I would say it's very much the kind of thing Jack would do. It would be deadly nightshade fanny cake or amanita soup.